Matlab turns char into double on cluster.

On the cluster I run

matlab -nodesktop -r "program 1" > program_1.out 2>&1 

where the first lines of code in "program" look like this

function program(dtaset_id)

addpath(genpath('../..'))

if isempty(gcp('nocreate'))
    parpool(maxNumCompThreads,'IdleTimeout', 300)
end

whos
load(strcat('dataset_', dtaset_id, '.mat'))
whos
dtaset_id = str2num(dtaset_id);

The strange thing is that the first "whos" reports "dtaset_id" to be a char, and the second whos reports it to be a double, causing an error in the last line.

How and why does this happen?

Answer 1

[Voss]

It may be that the mat file you load contains a variable called dtaset_id, which is a double. When you load the mat file that value overwrites the previous value of dtaset_id in your workspace.

Here I've attached a mat file with a double dtaset_id to demonstrate.

dtaset_id = '0';
whos('dtaset_id') % char

  Name           Size            Bytes  Class    Attributes

  dtaset_id      1x1                 2  char               

load(strcat('dataset_', dtaset_id, '.mat')) % overwrites dtaset_id with value from mat file
whos('dtaset_id') % now double

  Name           Size            Bytes  Class     Attributes

  dtaset_id      1x1                 8  double              

[Michael Stollenwerk]

Of course! That's it. Sorry, this one had me very puzzeled and as always in those cases its hiding in plain sight. Thanks!

[Stephen23]

This is one reason why it is recommended to always LOAD into an output variable:

S = load(..);